The present invention relates to projection display and recording devices, and in particular, to such projection display devices in which the projected images or patterns to be displayed are controlled by an electrophoretic type cell.
The use of electrophoresis in display devices containing a colloidal layer of suspended particles between electrodes has been previously contemplated, such as described in U.S. Pat. Nos. 3,612,758 and 3,668,106. These patents are hereby incorporated by reference to provide basic information of the chemistry and technology of electrophoretic displays.
A simple electrophoretic image display (EPID) device is a passive, light scattering-type display. This EPID device is constructed as a cell which consists of a colloidal suspension of pigment particles in an organic liquid held between two electrodes, at least one of which is transparent. In one operative mode, the pigment particles are negatively charged with respect to the liquid. If a positive potential is applied to an electrode in electrical contact with the suspension, the negatively charged pigment particles will be attracted to that electrode. A negative potential on an electrode repels the particles, to the opposite side of the cell.
One panel of the device is made of a transparent material such as glass, coated with a transparent, electrically-conducting layer forming one electrode. When light-colored pigment is attracted to this panel electrode, an observer looking at the panel sees the reflected color of the pigment. A dark-colored dye is included in the suspending medium so that pigment at the back of the cell is obscured by the opaque dye and the observer sees only the reflected color of the dye. When the polarity of the voltage on the electrodes is reversed, the position of the color is reversed. This EPID display cell also possesses "memory" since the particles remain on the electrodes after the applied voltages are removed due to chemical, electrical, or van der Waals forces.
Further, U.S. Pat. application Ser. No. 854,117 filed on Nov. 23, 1977, by Dalisa (the inventor of the present application) and Singer, and assigned to the Assignee of the present application, now U.S. Pat. No. 4,203,106, discloses EPID displays which are addressable and/or include electrode structures for establishing selective electric fields to transport suspended colloidal particles in the cell, and causing images to be formed by the presence or absence of particles at one of the electrode surfaces of the cell. This prior application is also hereby incorporated herein by reference.
Moreover, light transmissive electrophoretic image displays have been contemplated in which internally reflecting members are utilized to provide background illumination, as described in U.S. pat. application Ser. No. 63,634, filed on Aug. 2, 1979, now U.S. Pat. No. 4,218,302, by Dalisa (the inventor of the present application) and Seymour and assigned to the Assignee of the present application. This patent to Dalisa and Seymour is hereby incorporated herein by reference.
While such devices are highly desirable and provide a significant advance in the art, they are largely limited to direct viewing type devices. It is desirable in many instances to provide projection of the image formed by the EPID device to a remote viewing apparatus, and to operate in a reflection mode.